Openly porous carbon/carbon composite friction material formed of carbon fibrous substrate coated with pyrolytic carbon by chemical vapor deposition (CVD) is known in the prior art as may be seen by reference to U.S. Pat. Nos. 4,291,794 and 4,700,823. The disclosures of these documents are incorporated herein by reference.
Blocked, change gear transmissions of the single and compound type are also known in the prior art as may be seen in U.S. Pat. Nos. 3,983,979; 4,141,440; 4,176,736; and 4,703,667. The disclosures of these documents are also incorporated herein by reference.
Blocker-clutch assemblies used in these change gear transmissions include first and second positive or jaw clutches which are axially moved between engaged and disengaged positions to effect gear changes. Each assembly includes a frictionally engagable blocker ring which prevents asynchronous engagement of the jaw clutches in response to initial engaging movement thereof. The blocker ring is supported by the first jaw clutch for limited rotation relative thereto and includes a friction surface which engages a second friction surface, secured for rotation with the second jaw clutch, in response to the initial engaging movement of the jaw clutches. If the jaw clutches are rotating at different speeds during the initial engaging movement thereof, the frictional engagement effects limited rotation of the blocker ring to a position blocking engagement of the jaw clutches until substantial synchronization of the jaw clutches is achieved.
The above described blocker-clutch assemblies have greatly reduced the complexity and effort required to effect gear changes. However, for various surmised reasons the blocker rings have been known to prematurely move to the unblocking position before the jaw clutches reach synchronism or substantially synchronous speeds, thereby allowing asynchronous engagement of the jaw clutch teeth with resultant excessive wear thereto and in some cases failure of the jaw clutches. Providing at least on the friction surfaces with the above composite friction material has effectively solved premature unblocking, provided the material is properly bonded to the surface.